A study published in the March 2026 issue of Chronic Obstructive Pulmonary Diseases: Journal of the COPD Foundation examined the relationship between dietary isoflavone consumption and respiratory symptoms in former smokers with Chronic Obstructive Pulmonary Disease (COPD). The research found statistical associations between higher isoflavone intake and improved symptom scores, though causality was not established.
Study Design and Participants
The study used data from the urban arm of the CURE COPD study in Baltimore, Maryland. Participants included:
- Age 40 or older with physician-diagnosed moderate-to-severe COPD
- Former smokers with a history of more than 10 pack-years
- Low socioeconomic status
A total of 99 participants had complete data. The mean age was 66.4 years; 55% were female; 41% identified as White. The mean smoking history was 46.3 pack-years, and the mean FEV1 percent predicted (a measure of lung function) was 49.8%.
Dietary intake was assessed using the Harvard Food Frequency Questionnaire at baseline, three months, and six months. Respiratory outcomes were measured using validated questionnaires: the COPD Assessment Test (CAT), Clinical COPD Questionnaire (CCQ), and Evaluating Respiratory Symptoms in COPD (ECSC). Biomarkers were analyzed from blood and urine samples.
Key Findings
Participants with higher total isoflavone intake reported lower scores on the CAT, CCQ, and ECSC, indicating fewer respiratory symptoms and better health status.
- Each standard deviation increase in isoflavone intake corresponded to a 7.4% reduction in urinary 11-dehydrothromboxane B2 (11dTxB2), a marker of platelet activation.
- Specific isoflavones—daidzein, genistein, formononetin, and glycitein—showed associations with improved respiratory scores. Biochanin A did not show this association.
- The associations persisted after adjusting for omega-3 fatty acid intake and antiplatelet medication use, though the link with 11dTxB2 was attenuated.
Background
COPD, which includes emphysema and chronic bronchitis, is a progressive inflammatory lung disease affecting over 30 million Americans and is the fourth leading cause of death globally. Diet and nutrition are recognized as modifiable risk factors for chronic lung disease. Isoflavones are compounds commonly found in legumes and soy-based foods.
Researcher Statement
Daniel C. Belz, M.D., MPH, of the Division of Pulmonary and Critical Care Medicine at Johns Hopkins University and lead author, stated that further research is needed to identify specific nutritional components responsible for reducing symptoms of inflammatory conditions like COPD. He added that larger studies are necessary to explore how increasing isoflavone consumption might affect COPD symptoms and overall lung health.
Limitations
The study is observational, with a small sample size, reliance on self-reported dietary data, and limited biomarker analyses. As a result, causality cannot be established.